86 FKAGMENTS OF SCIENCE. 



the domain of sense, thought, or emotion, a definite 

 molecular condition, of motion or structure, is set up 

 in the brain ; or who would be disposed even to deny 

 that if the motion, or structure, be induced by internal 

 causes instead of external, the effect on consciousness 

 will be the same? Let any nerve, for example, be 

 thrown by morbid action into the precise state of 

 motion which would be communicated to it by the 

 pulses of a heated body, surely that nerve will declare 

 itself hot the mind will accept the subjective intima- 

 tion exactly as if it were objective. The retina may be 

 excited by purely mechanical means. A blow on the 

 eye causes a luminous flash, and the mere pressure of 

 the finger on the external ball produces a star of light, 

 which Newton compared to the circles on a peacock's 

 tail. Disease makes people see visions and dream 

 dreams ; but, in all such cases, could we examine the 

 organs implicated, we should, on philosophical grounds, 

 expect to find them in that precise molecular condition 

 which the real objects, if present, would superinduce. 



The relation of physics to consciousness being thus 

 invariable, it follows that, given the state of the brain, 

 the corresponding thought or feeling might be inferred: 

 or, given the thought or feeling, the corresponding state 

 of the brain might be inferred. But how inferred? 

 It would be at bottom not a case of logical inference at 

 all, but of empirical association. You may reply, that 

 many of the inferences of science are of this character 

 the inference, for example, that an electric current, 

 of a given direction, will deflect a magnetic needle in a 

 definite way. But the cases differ in this, that the 

 passage from the current to the needle, if not demon- 

 strable, is conceivable, and that we entertain no doubt 

 as to the final mechanical solution of the problem. 

 But the passage from the physics of the brain to the 



